Japanese beetles are alive and well and probably feeding on the plants in your yard. They feed on shrubs, turf grasses, and trees, leaving behind damaged plants.
The adult beetles appear in late June through September to feed, mate and lay eggs. The beetles are destructive, but treatments to control the larvae and the beetles are available.
It’s important to use the appropriate type of treatment to control the beetles. Many insecticides are ineffective when Japanese beetles are in the grub stage. In addition, some insecticides are harmful to bees, so the city encourages residents to consider alternatives to chemical insecticides.
If you see a moderate number of Japanese beetles, experts suggest they can be handpicked or knocked off into soapy water. This is more effective if done in the evening because Japanese beetles are active feeders at night.
Another option is to spray the lawn with two tablespoons of liquid dishwashing soap diluted in one gallon of water per 1,000 square feet of lawn. The grubs will come above ground and birds can eat them. Spray once each week until grubs no longer surface. Since beetles have two life cycles per season it is most effective if done in late spring and autumn when the beetles are in the grub stage.
Many types of birds, including grackles, meadowlarks, starlings, cardinals, pheasants, chickens, ducks, and geese feed on the Japanese beetles. Starlings, grackles, crows, and gulls eat the Japanese beetle larvae.
Milky spore disease is another alternative method of treatment. It is a safe bacterium that is applied to grass as a powder. It is effective only in controlling Japanese beetle grubs and works best when the soil temperatures are between 60° and 70° F. In cooler climates, milky spore takes longer to spread. Research has determined that milky spore has no impact on beneficial organisms in the soil. Visit the University of Illinois website to learn more about milky spore disease.
In addition, the University of Minnesota offers information about controlling Japanese beetles and other insects. Find information at www.extension.umn.edu/garden/insects or call the Minnesota Landscape Arboretum Yard and Garden line at 612-301-7590.